Electric field sensor

ABSTRACT

An electric field sensor comprises a sensor head 1, a package 13 accommodating the sensor head, and an antenna 14 attached to the outside of the package and connected to the sensor head 1. The sensor head 1 has a substrate 3 and an optical modulator 4 attached thereto. The optical modulator 4 has an incident optical waveguide 5 formed on the substrate 3, two phase-shift optical waveguides 6 which are formed on the substrate 3 to be branched from the incident optical waveguide 5 and each of which has a variable refractive index varying in response to an electric field intensity applied thereto, an outgoing optical waveguide 7 formed on the substrate 3 to join the phase-shift optical waveguides 6, and two modulation electrodes 8 formed on or in the vicinity of the phase-shift optical waveguides 6. The antenna 14 has two rod antenna elements 17 and 18. The rod antenna elements 17 and 18 extend in opposite directions with their one ends located at a center portion of the package 13 and are arranged in parallel to the phase-shift optical waveguides 6.

TECHNICAL FIELD

This invention relates to an electric field sensor for measuring anelectric field intensity of an electromagnetic wave or the like.

BACKGROUND ART

FIG. 1 shows a conventional electric field sensor. The electric fieldsensor comprises a sensor head 1 and an antenna 2 connected to thesensor head 1. The sensor head 1 has a substrate 3 and an opticalmodulator 4 attached to the substrate 3.

The optical modulator 4 comprises an incident optical waveguide 5 formedon the substrate 3, two phase-shift optical waveguides 6 which areformed on the substrate 3 to be branched from the incident opticalwaveguide 5 and each of which has a variable refractive index varying inresponse to an electric field intensity applied thereto, an outgoingoptical waveguide 7 formed on the substrate 3 to join the phase-shiftoptical waveguides 6, and two modulation electrodes 8 formed on or inthe vicinity f the phase-shift optical waveguides 6. The incidentoptical waveguide 5 is connected to an incident optical fiber 9. Theoutgoing optical waveguide 7 is connected to an outgoing optical fiber10.

The antenna 2 has two rod antenna elements 11. The rod antenna elements11 are connected through lead wires 12 to the modulation electrodes 8,respectively. The rod antenna elements 11 are arranged to face adirection of an electric field, in other words, to be perpendicular tothe phase-shift optical waveguides 6. The rod antenna elements 11 arefixed to a package which is not illustrated in the figure.

In the conventional electric field sensor, the antenna elements face thedirection of the electric field during measurement. Accordingly, adraw-out portion of the optical fiber faces a direction of measurement.This possibly results in a damage of the optical fiber.

In the conventional electric field sensor, the antenna must be arrangedin various directions during measurement because of its strictdirectivity.

It is an object of this invention to provide an electric field sensorcapable of preventing a damage of an optical fiber.

It is another object of this invention to provide an electric fieldsensor which need not be arranged in various directions duringmeasurement.

DISCLOSURE OF THE INVENTION

This invention comprises a sensor head having a substrate and an opticalmodulator attached to the substrate, a package accommodating the sensorhead, and an antenna attached to the outside of the package andconnected to the optical modulator. The optical modulator comprises twophase-shift optical waveguides each of which has a variable refractiveindex varying in response to an electric field intensity appliedthereto, and modulation electrodes formed on or in the vicinity of thephase-shift optical waveguides. The antenna has two rod antenna elementsrespectively connected to the modulation electrodes. The rod antennaelements extend in opposite directions with their one ends located at acenter portion of the package and are arranged in parallel to thephase-shift optical waveguides.

This invention may have a structure such that the antenna comprises twofilm antenna elements respectively connected to the modulationelectrodes and fixedly attached to a side surface of the package andthat the film antenna elements extend in opposite directions with theirone ends located at a center portion of the package and are arranged inparallel to the phase-shift optical waveguides.

This invention may have a structure such that the antenna comprises twofilm antenna elements respectively connected to the modulationelectrodes and formed on the substrate in parallel to the phase-shiftoptical waveguides.

Furthermore, this invention comprises a sensor head having a substrateand a plurality of optical modulators attached to the substrate, and aplurality of antennas respectively connected to the optical modulators.Each of the optical modulators comprises an incident optical waveguideformed on the substrate, two phase-shift optical waveguides which areformed on the substrate to be branched from the incident opticalwaveguide and each of which has a variable refractive index varying inresponse to an electric field intensity applied thereto, an outgoingoptical waveguide formed on the substrate to join the phase-shiftoptical waveguides, and modulation electrodes formed on or in thevicinity of the phase-shift optical waveguides. The antennas arerespectively connected to the modulation electrodes of a plurality ofthe optical modulators.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a conventional electric field sensor.

FIG. 2 is a plan view of one embodiment of this invention.

FIG. 3 is a perspective view of another embodiment of this invention.

FIG. 4 is a plan view of still another embodiment of this invention.

FIG. 5 is a plan view of a further embodiment of this invention.

FIG. 6 is a plan view of a still further embodiment of this invention.

FIG. 7 is a side view of the embodiment in FIG. 6.

FIG. 8 is a perspective view of a yet further embodiment of thisinvention.

EMBODIMENTS

Description will now be made in detail as regards embodiments of thisinvention with reference to the drawing.

As illustrated in FIG. 2, an electric field sensor according to, thisinvention comprises a sensor head 1, a package 13 accommodating thesensor head 1, and an antenna 14 attached to the outside of the package13 and connected to the sensor head 1. The sensor head 1 has a substrate3 and an optical modulator 4 attached to the substrate 3.

The optical modulator 4 comprises an incident optical waveguide 5 formedon the substrate 3, two phase-shift optical waveguides 6 which areformed on the substrate 3 to be branched from the incident opticalwaveguide 5 and each of which has a variable refractive index varying inresponse to an electric field intensity applied thereto, an outgoingoptical waveguide 7 formed on the substrate 3 to join the phase-shiftoptical waveguides 6, and to modulation electrodes 8 formed on or in thevicinity of the phase-shift optical waveguides 6.

The incident optical waveguide 5 is connected to an incident opticalfiber 9. The incident optical fiber 9 is connected to a light source 15.For example, the light source 15 comprises a semiconductor laser. Theoutgoing optical waveguide 7 is connected to an outgoing optical fiber10. The outgoing optical fiber 10 is connected to an optical detector16.

The antenna 14 comprises two rod antenna elements 17 and 18. The rodantenna elements 17 and 18 extend in opposite directions with their oneends located at a center portion of the package 13 and are arranged inparallel to the phase-shift optical waveguides 6. The rod antennaelements 17 and 18 are connected through lead wires 19 and 20 to themodulation electrodes 8, respectively.

A light beam from the light source 15 is incident through the incidentoptical fiber 9 to the incident optical waveguide 5 and branched by thetwo phase-shift optical waveguides 6 into branched beams which are againcombined together in the outgoing optical waveguide 7. The light beamafter being combined in the outgoing optical waveguide 7 is emittedthrough the outgoing optical fiber 10 to the optical detector 16. Whenthe antenna 14 receives a reception signal, the modulation electrodes 8apply predetermined electric fields to the phase-shift opticalwaveguides 6. Depending upon the intensities of the electric fields, therefractive indexes of the phase-shift optical waveguides 6 are varied.This results in variation of phases of the light beams transmittedthrough the phase-shift optical waveguides 6.

A more specific example of the electric field sensor illustrated in FIG.2 will be described hereinafter. The substrate 3 comprises a LiNbO₃plate. The incident optical waveguide 5, the phase-shift opticalwaveguides 6, and the outgoing optical waveguide 7 are formed by thermaldiffusion of Ti on a Z plane of the substrate 3. The incident opticalfiber 9 comprises a constant-polarization optical fiber.

Another embodiment illustrated in FIG. 3 has similar components depictedby the same reference numerals as those scribed in conjunction with theembodiment of FIG. 2. As illustrated in FIG. 3, the antenna 14 has twofilm antenna elements 22 and 23 fixedly attached to a side surface 21 ofthe package 13. The film antenna elements 22 and 23 extend in oppositedirections with their one ends located at a center portion of thepackage 13 and are arranged in parallel to the phase-shift opticalwaveguides 6. The film antenna elements 22 and 23 are connected throughlead wires 24 and 25 to the modulation electrodes 8, respectively.

With the electric field sensors according to the embodiments illustratedin FIGS. 2 and 3, it is possible to prevent a damage of the opticalfiber because the draw-out portion of the optical fiber connected to theelectric field sensor does not face the direction of measurement.

A still another embodiment illustrated in FIG. 4 has similar componentsdepicted by the same reference numerals as those described inconjunction with the embodiment of FIG. 2. As illustrated in FIG. 4, anantenna 26 has two film antenna elements 27 and 28 formed on thesubstrate 3 in parallel to the phase-shift optical waveguides 6. Thefilm antenna elements 27 and 28 are arranged on both sides of thephase-shift optical waveguides 6. The film antenna elements 27 and 28are connected through lead wires 29 and 30 to the modulation electrodes,respectively.

As illustrated in FIG. 5, the film antenna elements 27 and 28 may bearranged on one side of the phase-shift optical waveguides 6.

With the electric field sensor according to the embodiments illustratedin FIGS. 4 and 5, it is possible to prevent a damage of the opticalfiber because the draw-out portion of the optical fiber connected to theelectric field senor does not face the direction of measurement. Theelectric field sensor according to the embodiments in FIGS. 4 and 5 areadapted to achieve reduction of size

As illustrated in FIGS. 6 and 7, an electric field sensor according tothis invention comprises the sensor head 1, the package 13 accommodatingthe sensor head 1, and antennas 31, 32, and 33 attached to the outsideof the package 13 and connected to the sensor head 1.

The sensor head 1 comprises a substrate 3 and a plurality of opticalmodulators 34, 35, and 36 attached to the substrate 3.

Each of the optical modulators 34, 35, and 36 has the incident opticalwaveguide 5 formed on the substrate 3, the two phase-shift opticalwaveguides 6 which are formed on the substrate 3 to be branched from theincident optical waveguide 5 and each of which has a variable refractiveindex varying in response to the electric field intensity appliedthereto, the outgoing optical waveguide 7 formed on the substrate 3 tojoin the phase-shift optical waveguides 6, and the two modulationelectrodes 8 formed on or in the vicinity of the phase-shift opticalwaveguides 6.

The incident optical waveguide 5 is connected to the incident opticalfiber 9. The incident optical fiber 9 is connected to the light source15. The outgoing optical waveguide 7 is connected to the outgoingoptical fiber 10. The outgoing optical fiber 10 is connected to theoptical detector 16.

The antennas 31, 32, and 33 are arranged to be perpendicular to oneanother. The antennas 31, 32, and 33 are connected through the leadwires to the modulation electrodes 8 of the optical modulators 34, 35,and 36, respectively.

As illustrated in FIG. 8, each of the optical modulators 34, 35, and 36has the incident optical waveguide 5 formed on the substrate 3, the twophase-shift optical waveguides 6 which are formed on the substrate 3 tobe branched from the incident optical waveguide 5 and each of which hasa variable refractive index varying in response to the electric fieldintensity applied thereto, the outgoing optical waveguide 7 formed onthe substrate 3 to join the phase-shift optical waveguides 6, and thetwo modulation electrodes 8 formed on or in the vicinity of thephase-shift optical waveguides 6.

The sensor head 1 has a common incident optical waveguide 37 connectedto the incident optical fiber 9, primary branch optical waveguides 38and 39 formed on the substrate 3 to be branched from the common incidentoptical waveguide 37, secondary branch optical waveguides 40 and 41formed on the substrate 3 to be branched from the primary branch opticalwaveguide 38, and tertiary branch optical waveguides 42 and 43 formed onthe substrate 3 to be ranched from the primary branch optical waveguide39.

The secondary branch optical waveguide 40 is connected to the incidentoptical waveguide 5 of the optical modulator 24. The secondary branchoptical waveguide 41 is connected to the incident optical waveguide 5 ofthe optical modulator 35. The tertiary branch optical waveguide 42 isconnected to the incident optical waveguide 5 of the optical modulator36. The tertiary branch optical waveguide 43 is connected through theoutgoing optical fiber 10 to the optical detector 16. The light beamtransmitted through the tertiary branch optical waveguide 43 is emittedthrough the outgoing optical fiber 10 to the optical detector 16. Thelight beam transmitted through the tertiary optical waveguide 43 is usedas a reference light beam to monitor the light beam transmitted throughthe optical modulators 34, 35, and 36.

Each of the embodiments illustrated in FIGS. 6 through 8 has a pluralityof antennas. It is therefore unnecessary to change the orientation invarious directions during measurement. In addition, it is possible tocarry out measurement independent from the incoming direction of theelectromagnetic wave to be measured and from the polarization component.

Industrial Applicability

This invention is adapted for use in a device for measuring an intensityof an electric field such as an electromagnetic wave and electromagneticnoise.

We claim:
 1. An electric field sensor comprising a sensor head having asubstrate and an optical modulator attached to said substrate, a packageaccommodating said sensor head, and an antenna attached to the outsideof said package and connected to said optical modulator, said opticalmodulator comprising an incident optical waveguide formed on saidsubstrate, two phase-shift optical waveguides which are formed on saidsubstrate to be branched from said incident optical waveguide and eachof which has a variable refractive index varying in response to anelectric field intensity applied thereto, an outgoing optical waveguideformed on said substrate to join said phase-shift optical waveguides,and two modulation electrodes formed on or in the vicinity of saidphase-shift optical waveguides, said antenna having two rod antennaelements respectively connected to said modulation electrodes, said rodantenna elements extending in opposite directions with their one endslocated at a center portion of said package and being arranged inparallel to said phase-shift optical waveguides.
 2. An electric fieldsensor comprising a sensor head having a substrate and an opticalmodulator attached to said substrate, a package accommodating saidsensor head, and an antenna attached to the outside of said package andconnected to said optical modulator, said optical modulator comprisingan incident optical waveguide formed on said substrate, two phase-shiftoptical waveguides which are formed on said substrate to be branchedfrom said incident optical waveguide and each of which has a variablerefractive index varying in response to an electric field intensityapplied thereto, an outgoing optical waveguide formed on said substrateto join said phase-shift optical waveguides, and two modulationelectrodes formed on or in the vicinity of said phase-shift opticalwaveguides, said antenna having two film antenna elements respectivelyconnected to said modulation electrodes and fixedly attached to a sidesurface of said package, said film antenna elements extending inopposite directions with their one ends located at a center portion ofsaid package and being arranged in parallel to said phase-shift opticalwaveguides.
 3. An electric field sensor comprising a sensor head havinga substrate and an optical modulator attached to said substrate, and anantenna connected to said optical modulator, said optical modulatorcomprising an incident optical waveguide formed on said substrate, twophase-shift optical waveguides which are formed on said substrate to bebranched from said incident optical waveguide and each of which has avariable refractive index varying in response to an electric fieldintensity applied thereto, an outgoing optical waveguide formed on saidsubstrate to join said phase-shift optical waveguides, and twomodulation electrodes formed on or in the vicinity of said phase-shiftoptical waveguides, said antenna having two film antenna elementsrespectively connected to said modulation electrodes and arranged onsaid substrate in parallel to said phase-shift optical waveguides.
 4. Anelectric field sensor comprising a sensor head having a substrate and aplurality of optical modulators attached to said substrate, and aplurality of antennas respectively connected to said optical modulators,each of said optical modulators comprising an incident optical waveguideformed on said substrate, two phase-shift optical waveguides which areformed on said substrate to be branched from said incident opticalwaveguide and each of which has a variable refractive index varying inresponse to an electric field intensity applied thereto, an outgoingoptical waveguide formed on said substrate to join said phase-shiftoptical waveguides, and two modulation electrodes formed on or in thevicinity of sad phase-shift optical waveguides, said antennas beingrespectively connected to said modulation electrodes of a plurality ofsaid optical modulators.